1. Technical Field
The present invention relates to a method of making a hole in a substrate and a substrate, and specifically relates to a method of making a hole using etching.
2. Related Art
An ink jet method is widely used where ink is discharged from an ink jet head as liquid droplets and various patterns are drawn. The ink jet head discharging the ink includes a nozzle plate where a plurality of nozzle holes are formed to discharge ink droplets and a flow path forming substrate where a discharge chamber and an ink flow path are formed to communicate with the nozzle holes. In the ink jet head, a drive unit applies pressure to the discharge chamber and the ink droplets are discharged from selected nozzle holes. As the drive unit, there is an electrostatic drive system using an electrostatic force, a piezoelectric drive system using a piezoelectric element, a drive system using a heater element and the like.
JP-A-2010-158822 discloses a method of assembling a nozzle plate and a flow path forming substrate. According to the related art, a pair of positioning holes are disposed at the nozzle plate. One of the positioning holes is a regular octagonal reference hole and the other thereof is a long hole which is long in one direction. Thus, the positioning holes are also positioned at the flow path forming substrate. After aligning the positions by inserting a pin to the positioning holes of the nozzle plate and the flow path forming substrate, the nozzle plate and the flow path forming substrate are assembled. Accordingly, the nozzle plate and the flow path forming substrate can be assembled with high positional accuracy.
JP-A-2010-240852 discloses a method of manufacturing a nozzle plate. According to the related art, nozzle holes are configured such that a first nozzle of an outside air side and a second nozzle of a discharge chamber side are arranged coaxially. The diameter of the first nozzle is smaller than that of the second nozzle. Thus, after the first nozzle is formed on a surface of a substrate, a protection film is formed on the first nozzle. The protection film includes a function for separating front and back sides of the substrate, and the protection film is referred to as a separation film below. Next, the substrate is thinned by grinding the backside of the substrate. Subsequently, the second nozzle is formed at the backside of the substrate.
At this time, etching is performed on the substrate until the separation film is exposed. Next, the separation film, which is positioned between the second nozzle and the first nozzle, is removed. The nozzle holes are manufactured in the step and thereby the length of a hole of the first nozzle is formed with the high positional accuracy.
In order to manufacture the nozzle plate with good productivity, a method is considered where the positioning hole is formed concurrently with the first nozzle forming step and the second nozzle forming step. In other words, a portion of the positioning hole is formed during the first nozzle forming step. Next, the separation film is arranged and the substrate is thinned. Subsequently, a remaining portion of the positioning hole is formed during the second nozzle forming step. In the step, etching gas flows on the backside of the substrate and cooling gas flows on the frontside of the substrate. The etching gas and the cooling gas are separated by the separation film. Thus, when the separation film is exposed to the backside, the separation film receives pressure corresponding to the difference between pressure of the etching gas and pressure of the cooling gas. Accordingly, when the separation film is torn, becomes waste and attaches to the nozzle plate or a manufacturing apparatus, normal etching may not be performed and flaws may occur. A manufacturing method is preferable in which the hole separation film is not easy to tear in the process of manufacturing a hole where a plurality of holes of different sizes overlap.